Since the plasterboard, the refractory board and the veneer plywood are very brittle, the fastening force for holding the nails or the set screws driven into such a brittle plasterboard is very low and unstable, so that the nails or the set screws thus secured to the brittle wall tend to be loosened or detached when a load or a vibration is applied thereto. Therefore, such nails and set screws are not suitable for positively securing the fixing device to the brittle wall.
It has been proposed heretofore as shown in FIG. 47 to use a backplate 1 made of wood, for example, which is attached to the rear surface of the brittle plasterboard or the refractory board 2 at a predetermined position when nails or screws are used for securing the fixing device onto that portion of the board where the backplate is attached. Thus, the effective holding force is obtained when the article 3 shown as a hook is to be attached onto the board 2 by using the nails or the set screws 4 by virtue of the fact that the nails or the set screws 4 are driven into the backplate 1 having a sufficient holding force.
As an alternative measure for securing the fixing device onto the brittle plasterboard, it has been known to use an anchor bolt in place of the set screws and the nails. As an example of using the anchor bolt as shown in FIG. 48, an anchor member 6 is threadedly fitted on the bolt 5 as shown by the one dot chain line and the anchor member 6 is inserted into the holes 3a and 2a formed in the article 3 and the plasterboard 2 together with the bolt 5, respectively, so as to extend outwardly from the rear side of the board 2 and, thereafter, the bolt 5 is rotated relative to the anchor member 6 so that the portion of the anchor member 6 extending outwardly from the rear surface of the board 2 is axially compressed to expand radially as shown by the solid line thereby securing the article 3 tightly to the board 2.
FIG. 49 shows an alternative form of the anchor member. It is made of material such as a resilient plastic material and is formed with a plurality of spring-back arms 7a extending from the outer end of the stem 7 which is in turn integrally formed with a hook 3. The spring-back arms 7a are directed toward the hook 3 with radially expanding resilient force being given to the arms 7a, so that, after the stem 7 is inserted into the hole 2a of the board 2 and the arms 7a extend out of the rear side of the board 2, the arms 7a expand radially by their resilient forces and abut against the rear side of the board 2 to thereby secure the hook 3 to the board 2.
In such a prior art fixing device as shown in FIG. 47, however, a backplate 1 must be provided prior to the securing of the fixing device, thereby raising the cost, and, at the same time, the position of the board 2 to which the article 3 is to be secured is limited.
In the methods using an anchor bolt and an anchor member as shown in FIGS. 48 and 49, a relatively large hole 2a must be formed in the board 2, thereby requiring a tool such as a drill, and a sufficient space must be provided at the rear side of the board 2, and an undesired play tends to occur in the hole 2a. Further, a large hole 2a is left after the anchor bolt 5 is removed together with the anchor member 6 shown in FIG. 48, while the anchor member having the stem 7 and the spring-back arms 7a shown in FIG. 49 cannot be removed once it is secured to the board 2.
In the prior art fixing device using set screws or nails, attention is required for the operator as to in which direction they are to be driven so as to achieve a strong securing force, or relatively large set screws or nails must be used to obtain sufficient securing force. The set screws and the nails tend to be loosened and detached from the brittle board in a relatively short time, and a large hole or flaw is left in the board after the fixing device is removed, thereby deteriorating the appearance of the board.